1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device. More particularly, the present invention relates to a manufacturing method of a memory cell.
2. Description of Related Art
Along with the development of integrated circuits technology, the level of integration has to increase continuously in order to improve the device speed and functions. Take memory structure for example. When information electronic products (such as computers, mobile phones, digital cameras or personal digital assistants) are needed to process and store more and more data day by day, the storage capacities of the memory structures required by these information electronic products have to increase as well. With such conflicting demand for a larger storage capacity but a shrinking size of the memory structure, developing methods that are capable of producing a smaller memory device with a higher integration level of the device while maintaining a desirable quality of performance has been a major target for the industry.
A typical electronically erasable programmable read-only memory (EEPROM) employs a floating gate and a control gate made of doped polysilicon. When programming a memory structure, the electrons injected into the floating gate are uniformly distributed in the entire polysilicon floating gate layer. Nevertheless, as memory cells shrink, the capacitance area between the floating gate and the control gate has to shrink as well. As a result, the size of the drive current is usually insufficient to perform operations such as programming, erasing and reading.
Although the industry has developed double gate memory cells and tri-gate memory cells to overcome the above-mentioned issues and improve the electrical performance of the device. However, these types of memory cells are expensive to manufacture and the fabrication process are complex. Further, the throughput of such memory cells is low. Moreover, in tri-gate memory cells, current leakage occurs at the corners of such device, and current leakage is worsened when the device is operated under high electric field. As a result, the reliability and stability of the memory device lowers and decreasing the production yield.